HALO aims towards the development of a“Digital Aristotle”: a computer-based knowledge source for students and scientists, allowing scientific experts to formulate textbook knowledge in a knowledge base which students can consult by posing queries at the level of the American AP exams. The project is funded by Vulcan Inc. (Seattle), owned by Microsoft co-founder Paul G. Allen. In the current phase, which began in October 2004, two teams are implementing versions that will be tested in a user evaluation in 2006. The teams are led by SRI International and the German company Ontoprise. The OU belongs to the“DarkMatter” team, led by Ontoprise, which also includes Carnegie-Mellon University, DFKI, Georgia Institute of Technology, and Intelligent Software Components S.A. (ISOCO). OU's role in the project is to contribute to the Question Formation component, using a natural-language interface through which students can pose queries to the DarkMatter system.